The hydrodesulfurization of petroleum hydrocarbons is well-known in the art. It is also known to use catalyst compositions in such hydrodesulfurization processes comprising a supported hydrogenating component which is at least one member of the group consisting of Group VI-B and Group VIII metals in a form capable of promoting hydrogenation reactions. Especially effective catalysts for the purpose of such hydrodesulfurization reactions are those comprising molybdenum and two members of the iron group metals. Preferred catalysts of this class are those containing nickel, cobalt and molybdenum but other combinations of iron group metals and molybdenum such as iron-molybdenum-cobalt, nickel-molybdenum-iron, as well as combinations of nickel and molybdenum, cobalt and molybdenum, nickel and tungsten or other Group VI-B or Group VIII metals taken singly or in combination. The hydrogenating or desulfurizing components of such catalysts are employed in the sulfided form.
Although the hydrogenating components indicated above may be employed in any proportions with each other, especially effective catalysts are those in which the hydrogenating components are those in the group consisting of oxides and sulfides comprising (a) a combination of 2 to 25%, preferably 4 - 16% by weight molybdenum and at least two iron group metals where the iron group metals are present in such proportions that the atomic ratio of each iron group metal in respect to molybdenum is less than about 0.4 and (b) a combination of about 5 to 40%, preferably 10 to 25% of nickel and tungsten where the atomic ratio of tungsten to nickel is about 1:0.1 to 5, preferably 1:0.3 to 4.
The hydrogenating components are composited with a porous alumina support. The alumina support is normally shaped in the form of granules, pellets or balls, prior to impregnation. The catalyst composite, however, can be in the form of a powder such as is employed for fluid type operations.
Conventionally, in the preparation of the prior art catalyst composites, the hydrogenation component such as molybdenum is deposited on the support from an aqueous solution of salts such as ammonium molybdate, ammonium paramolybdate, molybdenum pentachloride or molybdenum oxalate. After filtering and drying the impregnant is calcined to convert it into the oxide. The carrier is then treated with an aqueous solution of the iron group metal salt followed by calcining. If a second iron group metal is employed, the second iron group metal can be deposited in like manner. Nitrates or acetates of the iron group metals are normally utilized although any water soluble salt which leaves no harmful residue can be employed.
If desired, the iron group metals and molybdenum can be deposited simultaneously, but are preferably deposited in sequence with intervening calcining. Simultaneous impregnation of the iron group metals has been found to be satisfactory. Calcining of the catalyst composite has been conducted by heating in air to a temperature of 800.degree. to 1600.degree. F.
In sulfiding the catalyst composite, conventionally the catalyst is treated with hydrogen sulfide or hydrogen and hydrogen sulfide mixture. A second and a more preferred method of sulfiding the catalyst composite comprises contacting the catalyst at the beginning of an onstream period with the sulfur-containing petroleum distillate at the same conditions to be employed at the start of the desulfurization period. For example, if the desulfurization process is to be conducted initially at a temperature of 620.degree. F., the catalyst composite would be sulfided by contact with the sulfur-containing petroleum distillate at a temperature of 620.degree. F.
A disadvantage of employing the petroleum distillate feed in sulfiding the catalyst composite in the conventional manner is that initially the desulfurization activity of the catalyst composite is low. For example, where a desulfurization catalyst composite is employed for light petroleum distillate desulfurization it has been observed that only 65% of the sulfur is removed from the feed after two days of operation under hydrodesulfurization conditions at a temperature of 620.degree. F. When operating the desulfurization process at a temperature of 620.degree. F., equilibrium conditions where at least 70% of the sulfur is removed are not reached until a period of at least 10 days has lapsed.
Accordingly, an object of the invention is to provide an improved process for sulfiding a hydrodesulfurization catalyst.
Another object of the invention is to provide an improved process for sulfiding a hydrodesulfurization catalyst composite employing the sulfur-containing petroleum distillate feed in the sulfiding process.
Yet another object of the invention is to provide an improved hydrodesulfurization process operating at a temperature below 650.degree.F.
Other objects, advantages, and features of this invention will be readily apparent to those skilled in the art from the following description and appended claims.